DNA Study Confirms That This Bizarre Venomous Mammal Diverged From Other Mammals Long Before The Extinction Of The Dinosaurs

Watch your fingers – they bite! Seb_az86556/Wikimedia Commons; CC BY-SA 3.0
Robin Andrews 03 May 2016, 23:59

There’s a good chance that you’ve never heard of the solenodon before, and even if you have, you’re incredibly unlikely to have ever seen one in the flesh. These placental mammals, which are only found on the islands of Cuba and Hispaniola, physically resemble portly shrews with long, flexible noses and tails. They’re also extremely venomous, which is a thoroughly rare ability for a mammal of any sort to possess.

Although researchers know that these unusual critters have a fairly ancient evolutionary lineage, they were never sure just how old it really was. Now, a new study published in the journal Mitochondrial DNA by researchers at the Universities of Illinois and Puerto Rico reveals that they’ve managed to get their hands on some mitochondrial DNA from the Hispaniolan solenodon (Solenodon paradoxus).

After completely sequencing it, they have concluded that it diverged from all other living mammals 78 million years ago. This means that it has outlasted a remarkable range of environmental nadirs, including the apocalypse that is thought to have finished off the non-avian dinosaurs.

Interestingly, some are blaming mammals like the solenodon for initially pushing dinosaurs towards extinction; this dating confirms it was indeed around during the global decline of dinosaurian species.

“It's just impressive it's survived this long,” co-first author Adam Brandt, a postdoctoral researcher at Illinois, said in a statement. “It survived the asteroid; it survived human colonization and the rats and mice humans brought with them that wiped out the solenodon's closest relatives.”

Some blood is drawn from a venomous, Pokémon-esque solenodon at night. Taras Oleksyk and Yashira Afanador.

The island of Hispaniola is the only place that you’ll find the eponymous species of solenodon. These hedgehog-like animals are hard to find as they’re both nocturnal and endangered, and even if you do find one, they can be quite dangerous. Unlike the duck-billed platypus, they can physically inject their rarified venom into a victim through specially designed fangs.

For this study, the team of researchers managed to track down one of these animals and extract some of its mitochondrial DNA. The only way to do this was to lay down on the ground and take genetic samples as the solenodons – which apparently reek of sweaty goats – crawled over them.  

Unlike nuclear DNA, which is a mixture of genes from each parent, the mitochondrial DNA is only passed down from the mother to her offspring with almost no changes. Thankfully, this means that researchers can use this DNA to track the genetic history of an organism and its wider family.

Using two different methods to determine the sequence of nucleotides – the DNA building blocks – of the mitochondrial genome, they were able to precisely match it to the last common mammalian ancestor whose mitochondrial DNA is also known. Their results, which agree with other genetics studies, suggest it diverged from ancient mammals 12 million years before the non-avian dinosaurs went extinct.

This study fills in the last major branch of how placental mammals fit on the tree of life. How they actually first got onto Hispaniola is, however, less clear. “Whether they got on the island when the West Indies ran into Mexico 75 million years ago, or whether they floated over on driftwood or whatever else much later is not very clear,” added study coordinator Alfred Roca, a professor of animal sciences at the University of Illinois.

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